The advent of rare-earth permanent magnets (REPM) has brought the realization of novel magnetic structures that are not practicable otherwise. So different are these remarkable materials from the earlier magnets that conventional design wisdom is inadequate to fully exploit their unique characteristics. Indeed, the conventional wisdom can lead to error or to the employment of cumbersome procedures that are quite unnecessary for REPM's. The salutary characteristics stem from two basic attributes of rare earth materials: (1) large intrinsic moments per unit volume, and (2) extraordinarily high resistance to demagnetization by external or internal demagnetization fields. The approaches to magnetic design fall into four broad main types: (1) analogy of magnetic configurations to electrical circuits, (2) analytical solutions through Maxwell's equations, (3) reduction of permanent magnet arrays to distributions of pole densities or current sheets and inserting these distributions into Coulomb's law or the Biot-Savart law, and (4) brute-force computer solution of a tentative configuration (via two- or three-dimensional finite element analysis). We discuss all these approaches and employ them to solve illustrative examples.

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